Even in the era of computerised auto-pilots and smart bombs, flying a combat helicopter is a challenging job.

Like rubbing your tummy and tapping your head while travelling at 200 mph and banking hard right to avoid incoming enemy fire, the need to balance engine power, your helicopter's height above the ground, and the angle of attack of 25-metres of spinning rotor blades requires rigorous training and strong nerves.

Even simplified as tilts of an iPhone, iPod touch, or iPad, in gunship game Chopper 2 you have to have your wits about you.

Apache brave

The reason the controls - set to accelerometer by default with an alternate touch configuration available - are vital is that your vulnerability to ground fire is one of the game's sharpest elements.

Depending on whether you're being shot at by a tank or SAM-wielding soldier, you're only ever one or two hits away from being shot down and having to restart the level. The situation isn't helped by the fact that only way you can repair your damaged chopper is to fly back to a base.

As well as health, this will also rearm your supply of eight bombs and eight missiles. You have a machine gun backed by an unlimited supply of ammunition, too.

Since each level has to be completed within a certain time, the weakness of your helicopter, combined with the likelihood in many levels that you'll run out of time if you go for more than one repair, means there's little room for error, even when you're playing on of the lowest of three difficulty settings.

Blackhawk down

There are four basic locations - Desert, Snow, Forest, and City - each of which contains three sets of three missions, which have to be unlocked in sequence.

Strangely, though, you can't save your progress within each single set of three missions. In some ways, this doesn't matter unless you actively decide to exit to the main menu to break that set: the mission you're currently attempting will still be available when you restart the game. Still, it's an odd restriction.

It's worth mentioning because of the trouble I had with the second set of desert missions. During an escort mission in which you accompany a group of two jeeps protected by two tanks from one side of the level to the other, everything had to be executed perfectly. While not disputing my average abilities as a gamer, it took me over two hours and 50 attempts to complete.

By far the most difficult mission in the game, it underlines the fact that despite first impressions, Chopper 2 isn't a pick-up-and-play experience. This is a game that challenges you to spend time honing your skills and replaying levels.Jolly green giant

It's something that's built into the high scores, which are based both on the time taken to complete each level and the number of attempts you take. This feeds into a robust set of OpenFeint achievements and leaderboards.

If you're prepared to dig deep and overcome the game's stiff challenges, it has plenty to offer. The graphics have been massively improved. Everything from the models to the scenery is 3D, making for some highly impressive vistas. The ambient soundtrack and cinematics are neatly handled, too.

Variety is another of the game's strengths. From picking up civilians and dropping off computer specialists to defending bases, completing speed runs, and just generally blowing thing up, you're sure to never go bored.

How does this thing fly?

The ability to play on any iOS device is also welcome. Personally, I found using the iPad too unwieldy, but if you own an iPad and iPhone, you should be playing using the Bluetooth option in which your iPad acts a screen and iPhone as a controller. It works brilliantly, although as a minor point you can't sync your save games between devices.

Perhaps the most impressive thing about Chopper 2 is that, like the original, it's almost entirely the work of one-man band developer David Frampton.

It's a labour of love, and his dedication explains the game's steep difficulty. Yet it also ensures that when you do strap yourself into the armoured seat, fire up the rotors, and let rip with the Gatling gun you won't be disappointed.